1. Field of the Invention
The present invention generally relates to a communication system for transmitting/receiving data in accordance with an automatic repeat request (ARQ) protocol. More specifically, the present invention is directed to a method and a system, capable of automatically setting an optimum number of waiting frames (RTF) defined by that after an arbitrary frame has been transmitted to a receiving apparatus, this arbitrary frame is to be retransmitted due to no response from the receiving apparatus.
2. Description of the Related Art
The number of waiting frames (RTF) in the communication system for transmitting/receiving data based upon the automatic repeat request (ARQ) protocol is the waiting time at a transmission apparatus after a certain frame has been transmitted to a receiving apparatus until this frame is retransmitted due to no response from the receiving apparatus. This is regarded as the transmitted frame having not been received at the receiving apparatus, and this waiting time is calculated as the number of frames to be transmitted normally during the waiting time.
For example, when a communication is established between a transmitting apparatus and a receiving apparatus, and the transmitting apparatus cannot receive a confirmation frame of a certain transmitted frame from the receiving apparatus even after the time equivalent to the transmission time of one frame less than RTF has elapsed, the transmitting apparatus judges that the transmitted frame has not been received by the receiving apparatus. Then, the transmitting apparatus again transmits the same frame to the receiving apparatus.
In this manner, the frame retransmission between the apparatuses A and B is controlled with consideration of transmission delay between two apparatuses.
If the RTF is not suitably set, and it is set shorter than necessary waiting frames, the following protocol failure occurs. That is, the transmitting apparatus transmits a certain frame "n", and then, it is received by the receiving apparatus which will in turn transmit the confirmation frame of the transmitted frame "n". This is normal operation and the receiving apparatus is expecting to receive the next transmitted frame "m" from the transmitting apparatus. However, as the RTF being set in the transmitting apparatus is shorter than a transmission delay between those two apparatuses, the confirmation frame of the transmitted frame "n" from the receiving apparatus does not reach to the transmitting apparatus within a time period defined by the RTF, and it causes the transmitting apparatus to transmit the same frame "n" to the receiving apparatus, although the receiving apparatus is expecting the next frame "m".
Therefore, the fixed value long enough to prevent such protocol failure from ocurring in any combination of apparatuses in the communication network is set for the RTF. The fixed value is decided by considering the maximum transmission delay, including processing time of the protocol at the receiving apparatus and other signal buffering time of the hardware concerned for the communication between arbitrary apparatuses in the communication network, and has usually twice as much as the maximum transmission delay.
Accordingly, conventional technology of a retransmission of frame judged by the fixed value of RTF causes processing delay to increase in the case of data communication between apparatuses having a small value of transmission delay. In such a case, the RTF value is too long to wait for the retransmission of frame considering actual transmission delay between apparatuses. However, if the RTF is set to be a small value in order to reduce the delay in the process operation, protocol failure may occur as the foregoing in certain cases have a long transmission delay between apparatuses.